Underworld's position in the budding electronic universe : Each of its songs is as much a pop tune as a deftly sculpted rhythm track. Not the usual three-minute pop, but interwoven epics that develop over twice the length, using rhythms and loops rather than verses and choruses as building blocks. On SECOND TOUGHEST IN THE INFANTS (a nod to the hardships of sophomore outings), Karl Hyde, Rick Smith and Darren Emerson create a haunting new language built of dub, ambient, techno, jungle and rock textures, all set to a bass-heavy pulse. And even that fails to describe the dark, dreamlike atmospheres that the trio creates.